1. Field of the Invention
The present invention relates to a color lighting apparatus and method for illuminating color beams by separating white light emitted from a light source into several color beams and an image projection method and apparatus using the same. More particularly, the present invention relates to a small optical color lighting apparatus and method for illuminating color beams having high optical efficiency, and an image projection apparatus and method using the same.
2. Description of the Related Art
Generally, image projection systems provide images by projecting an image using a micro display, such as a liquid crystal display or a digital micromirror display, on a screen using a light source.
The image projection systems are classified into single-panel image projection systems and 3-panel image projection systems, according to the number of micro displays. The 3-panel image projection systems include three micro displays which are disposed on optical paths of separated red, blue, and green beams, respectively. Thus, the 3-panel image projection system has a higher optical efficiency than a single-panel image projection system, but its optical structure is more complicated, resulting in higher manufacturing costs.
Meanwhile, general single-panel image projection systems periodically separate white light emitted from a light source into red, blue, and green beams using a color wheel filter. The single-panel image projection systems have a more simpler optical structure than the 3-panel image projection systems, but have ⅔ more light loss than the 3-panel image projection systems due to the use of the color wheel filter, resulting in a reduced optical efficiency. A conventional image projection system, which uses a single-panel image projection system but solves the problem of the low optical efficiency, is illustrated in FIG. 1.
As illustrated in FIG. 1, the conventional single-panel image projection system includes a light source 11 for generating and irradiating non-polarized white light. The irradiated white light is converted into uniform light after passing through a fly eye lens array 13, which transforms incident light into uniform light by mixing the incident light, and then proceeds to a polarizing converter 15. The polarizing converter 15 changes the polarization of the non-polarized white light, irradiated from the light source 11, so that the non-polarized white light has a single polarization direction. The white light passed through the polarizing converter 15 is separated into red (R), green (G), and blue (B) beams by passing through first and second dichroic mirrors 17 and 19. Specifically, the first dichroic mirror 17 reflects only a color beam in the blue wavelength spectrum of the incident white light and transmits all other color beams. Next, the second dichroic mirror 19 separates the transmitted color beams into red and green beams, and similarly only transmits one of the colors.
First, second, and third scanning prisms 21, 23 and 25, for periodically scrolling incident light, are disposed along the respective optical paths of the separated R, G, and B beams. The first, second, and third scanning prisms 21, 23, and 25 may be square pillar-shaped prisms and rotatably driven by a driving unit (not shown). Angles between optical axes on the optical paths of the R, G, and B beams and sidewalls of the prisms 21, 23 and 25, change due to the rotatable drive of the first, second, and third scanning prisms 21, 23, and 25 so that the travel path of the beams passing through the prisms 21, 23, and 25 changes periodically.
Here, the initial angles of the first, second, and third scanning prisms 21, 23, and 25 are set such that the light passing through the prisms 21, 23, and 25 separates an effective image area of a display device 33 into three areas. Light passing through the prisms 21, 23 and 25 is then irradiated onto the three effective image areas, when the first, second, and third scanning prisms 21, 23 and 25 are rotatably driven along the optical paths of the R, G, and B beams. Thus, as illustrated in FIG. 2, the beams are focused onto the separated three areas while repeating a (B, R, G), (G, B, R), and (R, G, B) ordering according to the driven state of the prisms 21, 23 and 25.
The ordered beams exiting the first, second, and third scanning prisms 21, 23, and 25 are combined after passing though third and fourth dichroic mirrors 27 and 29. Here, reflecting mirrors 18 and 20, for changing the travel path of light, are disposed between the first and third dichroic mirrors 17 and 27 and between the second and fourth dichroic mirrors 19 and 29, respectively.
The scrolled light passing through the fourth dichroic mirror 29 is incident on a polarized beam splitter 31, which transmits or reflects incident light according to its polarization direction. As illustrated in FIG. 2, light reflected from the polarized beam splitter 31 is scrolled periodically and incident on the display device 33. The display device 33 forms an image from the incident light. Here, the image is produced by changing the polarization direction of the incident light on each pixel.
That is, only incident light whose polarization direction changes can pass through the polarized beam splitter 31 and proceed to a projection lens unit 35. The image incident on the projection lens unit 35 is then magnified and projected onto a screen 50.
The image projection system also includes a plurality of relay lenses 41, 42, 43, 44, 45, 46, 47 and 48 which are disposed along the optical path of light and transfer the incident light irradiated from the light source 11 to the display device 33.
Although only one display device is used in the conventional image projection system having the above structure, the optical structure of the image projection system is very complicated. Further, since the three scanning prisms rotate and scroll light independently, it is difficult to synchronize the image projection system with the display device.